Full-scale Municipal Solid Waste Incinerator Research Articles

Long-term implications of municipal solid waste (MSW) classification on emissions of PCDD/Fs and other pollutants: Five-year field study in a full-scale MSW incinerator in southern China

Understanding how municipal solid waste (MSW) classification influences the physiochemical properties and incineration emission characteristics of MSW is imperative for sustainable waste management. To investigate how long-term changes in the composition and physical properties of MSW resulting from MSW classification affect the emissions of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and multiple flue gas pollutants, a five-year experiment (2018–2022) was conducted in a full-scale MSW incinerator in Shenzhen City, China. After MSW classification, the food waste in MSW was substantially reduced while the paper, textile, and wood components were notably increased. MSW classification also remarkably decreased the water and chlorine contents of MSW while concomitantly increasing the wet-based calorific value, sulfur content, and nitrogen content. Consequently, the PCDD/Fs emissions declined from 106.7 ng I-TEQ/t MSW in 2018 to 26.0 ng I-TEQ/t MSW in 2022. Moreover, a process-tracing experiment demonstrated noticeable decreases in PCDD/F synthesis in the post-combustion area, with mass-reduction efficiencies of 23.6 %–95.4 %. In a correlation analysis, the PCDD/F emissions were significantly positively correlated with food waste, water content, and chlorine and negatively correlated with the wet-based calorific value and nitrogen content. Furthermore, MSW classification reduced the emissions of conventional flue gas pollutants (SO2, CO, and HCl) and multiple heavy metals (total sum of Sb, As, Pb, Cr, Co, Cu, Mn, and Ni). In summary, the long-term study demonstrated that MSW classification can feasibly separate incombustible waste, improve combustion quality, and reduce pollutant emissions from sources. These findings offer practical guidance for promoting MSW classification.

Inhibitory Effect and Mechanism of an N-S-Based Inhibitor (CH4N2S) on PCDD/Fs in Flue Gas and Fly Ash in a Full-Scale Municipal Solid Waste Incinerator

Inhibitory Effect and Mechanism of an N-S-Based Inhibitor (CH₄N₂S) on PCDD/Fs in Flue Gas and Fly Ash in a Full-Scale Municipal Solid Waste Incinerator

Dioxin emission prediction from a full-scale municipal solid waste incinerator: Deep learning model in time-series input

The immeasurability of real-time dioxin emissions is the principal limitation to controlling and reducing dioxin emissions in municipal solid waste incineration (MSWI). Existing methods for dioxin emissions prediction are based on machine learning with inadequate dioxin datasets. In this study, the deep learning models are trained through larger online dioxin emissions data from a waste incinerator to predict real-time dioxin emissions. First, data are collected and the operating data are preprocessed. Then, the dioxin emission prediction performance of the machine learning and deep learning models, including long short-term memory (LSTM) and convolutional neural networks (CNN), with normal input and time-series input are compared. We evaluate the applicability of each model and find that the performance of the deep learning models (LSTM and CNN) has improved by 36.5% and 30.4%, respectively, in terms of the mean square error (MSE) with the time-series input. Moreover, through feature analysis, we find that temperature, airflow, and time dimension are considerable for dioxin prediction. The results are meaningful for optimizing the control of dioxins from MSWI.

The co-removal of PCDD/Fs by SCR system in a full-scale municipal solid waste incinerator: Migration-transformation and decomposition pathways

The co-removal of PCDD/Fs by SCR system in a full-scale municipal solid waste incinerator: Migration-transformation and decomposition pathways

Characteristics of polychlorinated dibenzodioxins/dibenzofurans from a full-scale municipal solid waste (MSW) incinerator in China by MSW classification

The physical and chemical compositions of municipal solid waste (MSW) are important factors affecting the formation and release of polychlorinated dibenzodioxins/dibenzofurans (PCDD/Fs). A 4-year investigation (2017–2020) of the emission characteristics of PCDD/Fs from the flue gas and fly ash by a full-scale MSW incinerator in Ningbo city, Zhejiang province was conducted. This was undertaken to determine the implications of sorting MSW. Results showed that progress made in classifying MSW has led to a significant decrease in the proportion of kitchen waste components, the moisture and chlorine contents of MSW. However, there has also been a significant increase in the proportion of textile and wood components and calorific value. Approximately 60% of the PCDD/Fs generated during MSW incineration were captured in the fly ash that enters the filter bag. The PCDD/Fs emission factors were significantly positively correlated with the proportion of kitchen waste, plastics and heavy metal elements Fe, Ni, Mn, Cr, Pb, Cd, and Zn in the MSW, and negatively correlated with the wet-based high and low calorific values of the MSW. A decreasing trend in PCDD/Fs generation and emission from 3339.3 ng/t MSW in 2018–1787.5 ng/t MSW in 2020 was observed since the implementation of MSW classification as it can reduce the quantity of kitchen waste and plastics, and improve the calorific value of the MSW.

Emission levels and phase distributions of PCDD/Fs in a full-scale municipal solid waste incinerator: The impact of wet scrubber system

The emission of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from municipal solid waste (MSW) incinerations will pose serious risk to ecological environment and human health. To further understand the memory effect of wet scrubber system (WSS) on PCDD/Fs emission and phase distribution characteristics, a field study was conducted in a full-scale (850 t d−1) MSW incinerator where a WSS was newly adopted. The four exhaust flue gas samples and the two scrubbing solution samples inside WSS were separately collected for PCDD/Fs analyzing. The results indicated that the memory effect of WSS obviously enhanced the I-TEQ concentration of PCDD/Fs from 0.007 to 0.033 ng I-TEQ Nm−3 after flue gas passed through WSS, owing to increasing the total mass concentration of PCDD/Fs and the proportion of low-chlorinated congeners. The gas-phase PCDD/Fs was dominant (62.5%–88.9%) in flue gas, among which the PCDD/Fs enriched in condensed water notably contributed to nonnegligible proportions of 25.0%–67.6%. The adsorption/desorption process of PCDD/Fs was considered as one of the reasonable mechanisms of memory effect, based on the PCDD/Fs phase distribution and the congeners profile inside the WSS. Besides, the I-TEQ concentration of PCDD/Fs determined in scrubbing solution was up to 50.2 pg I-TEQ L−1, which might be a potential source to cause the enhancement of PCDD/Fs emission. This study verified the enhancement impact of WSS on PCDD/Fs emission and inspired the optimal design of WSS, i.e., choosing more suitable filling materials and timely replacing them to reduce the negative impact of memory effect, keeping WSS operated in relatively stable and consistent conditions, and safely disposing the scrubbing solution to mitigate the secondary pollution of PCDD/Fs.

Generalized prediction and optimal operating parameters of PCDD/F emissions by explainable Bayesian support vector regression.

The current derived models for predicting polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) emissions from incineration can only be applied to a specific incinerator due to high deviation or systematic errors. And the models fail to provide quantized guidance for the operation of full-scale municipal solid waste incinerators. To address the problem, explainable Bayesian support vector regression (E-BSVR) has been established to generalized predict and maximumly reduce the PCDD/F emissions. First, forty-two PCDD/F samples were determined from a whole year experiment in a full-scale incinerator. Meanwhile, 1,2,4-trichlorobenzene(1,2,4-TrCBz), carbon monoxide, sulfur dioxide, oxynitride, particulate matter, fluoride, and hydrogen chloride were measured, as input features. Second, after box-cox transformation normalization, and hyperparameters tuning, the R-Squared and root mean square error (RMSE) of the proposed method are 0.983 and 0.044, exhibiting high accuracy. The high accuracy (R-Squared=0.992) and generalization are also proven on the dataset with high PCDD/F emissions. Then, the performances of BSVR are compared with kernel ridge regression, multiple linear regression, and unary linear regression, indicating afar smaller RMSE of BSVR. Finally, the optimal operating parameters are calculated through local interpretable model-agnostic explanations and the partial dependence plot. Results indicate that reducing the content of organic chlorine in municipal solid waste and inhibiting the deacon reaction are important methods for reducing PCDD/F emissions. The optimal operating parameters for the maximal reduction of PCDD/F emissions are 1,2,4-TrCBz<0.098 ug/m3, fluoride>0.452mg/m3. As a whole, the E-BSVR method can be used as a reliable and accurate approach for the prediction and reduction of PCDD/F emissions.

Effects of evaporation capacity on the formation and removal of PCDD/Fs in a full-scale municipal solid waste incinerator

Municipal solid waste (MSW) classification has become a hot topic with the requirement of “zero waste city”; however, incinerators are designed unclassified currently. Therefore, it is difficult to keep around the rated value of evaporation capacity. Herein, we investigated the effects of evaporation capacity on the formation and removal of PCDD/Fs in a full-scale incinerator firstly. The formation of PCDD/Fs at the 110 % evaporation was lower than that of 100 % from the primary superheater to economizer, as high oxygen concentration. After flue gas flowed through the position of activated carbon injection, PCDD/F emissions at the 100 % evaporation were lower than that at the 110 % as the primary air volume at 110 % was 1.21 times that of 100 %. It had no significant effects on the PCDD/F emissions of the stack gas for an increase approximate 10 % of the evaporation capacity. Although the removal efficiencies of PCDD/F congeners varied in the four parts of the air pollution control devices (APCDs), while it was similar for the effects of APCDs on the removal efficiencies of PCDD/Fs between the two operating conditions. For the two different operating conditions, the removal efficiencies of congeners were kept at high levels (96.32–99.81 %) after flue gas flowed through APCDs and the removal efficiencies of the less-chlorinated congeners general were higher than those in the more-chlorinated congeners. And the removal efficiencies of PCDFs were much higher than PCDDs. These findings provide some new option for controlling PCDD/F emissions in a full-scale incinerator under the MSW classification.

Process tracing and partitioning behaviors of PCDD/Fs in the post-combustion zone from a full-scale municipal solid waste incinerator in southern China

Understanding the distributions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) throughout the full − scale municipal solid waste incinerator (MSWI) process is essential for controlling their emissions. In this study, we traced PCDD/Fs from an economizer to stack in the views of emission characteristics and partitioning behaviors. The results indicated that combining a vertical economizer with an ash hopper could remove PCDD/Fs from flue gas with a removal efficiency of 59.83%. In stack, the PCDD/Fs emissions in the liquid phase were 16.20 ng I-TEQ/t MSW, which was 53.67% of the total PCDD/Fs emissions. The PCDD/Fs in the liquid phase mainly originated from fine particles. The memory effect mainly occurred in the economizer, followed by the semi-dry scrubber and selective catalytic reduction. De novo synthesis dominated the formation of PCDD/Fs, while precursor formation and memory effect resulted in the PCDFs/PCDDs ratio following complex trends. These findings provide new information for constraining PCDD/Fs emissions in the full-scale MSWI.

The Co-Removal of Pcdd/Fs by Scr System in a Full-Scale Municipal Solid Waste Incinerator: Transformation and Decomposition Mechanism

The Co-Removal of Pcdd/Fs by Scr System in a Full-Scale Municipal Solid Waste Incinerator: Transformation and Decomposition Mechanism

Effect of different air pollution control devices on the gas/solid-phase distribution of PCDD/F in a full-scale municipal solid waste incinerator

The emission of polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) from full-scale municipal solid waste incinerators (MSWI) is harmful to human and environmental health. This study analyzes the effect of different units of an air pollution control devices (APCDs), i.e. the semi-dry scrubber, fabric filter (FF), selective catalytic reduction (SCR), and wet scrubber (WS), on the removal characteristics and gas- and solid-phase distributions of PCDD/F in MSWI flue gas. APCDs reduce PCDD/F concentrations from 24.9 ng Nm−3 to 0.979 ng Nm−3 (2.16 ng I-TEQ Nm−3 to 0.0607 ng I-TEQ Nm−3), with a total removal efficiency (RE) of 96.1% (97.2% I-TEQ). Specifically, APCDs remove more than 95% of both gas- and solid-phase PCDD/F. The FF coupled with active carbon injection (FF + ACI) substantially reduces both gas- and solid-phase PCDD/F concentrations with an RE of 97.2% (98.7% I-TEQ). Additionally, FF + ACI exhibits a better RE of PCDF (98.9%) than PCDD (94.6%) and leads to PCDD congeners dominating the gas-phase. Both desorption and destruction of PCDD/F occur in the SCR, which favors removal of gas-phase PCDD/F but increases solid-phase PCDD/F. Therefore, SCR only decreases PCDD/F with a low RE of 27.6% (16.9% I-TEQ). However, SCR reduces NOx with a high RE of 82.3%, which could inhibit the RE of PCDD/F because of their different reaction mechanisms. WS increases PCDD/F in both the gas and solid-phase by 1.95 times (2.57 times for I-TEQ) due to the memory effect, which typically increases the total mass concentration of PCDD/F and the proportions of lower-chlorinated gas-phase PCDD/F. Migration of gas- and solid-phase PCDD/F are also analyzed according to temperature. The results of this study can contribute to the optimized design of industrial APCDs for controlling PCDD/F emissions from MSWI.

PCDD/F levels and phase distributions in a full-scale municipal solid waste incinerator with co-incinerating sewage sludge

Co-incinerating sewage sludge in municipal solid waste incinerators (MSWIs) is an up-to-date disposal way with great prospects to market. To verify the environmental safety of this disposal method, a field study was conducted in a MSWI which has achieved PCDD/Fs ultra-low emission. PCDD/F phase partitioning characteristics, congener profiles, and the influence of selective catalytic reduction (SCR) were also investigated. PCDD/F emission levels ranged from 0.0031 to 0.0053 ng I-TEQ/Nm3, distinctly lower than the national standard. For tests co-incinerating 5% sludge, PCDD/F emission levels were averagely 32% lower than tests mono-combusting municipal solid waste. The phase partitioning study found that PCDD/Fs enriched in condensed water took a non-negligible proportion of the total concentration in flue gas. The removal efficiency of SCR in tests co-incinerating sludge was averaged at 41.9%. However, in tests without adding sewage sludge, PCDD/F concentrations in flus gas after SCR were increased. It was found that the elevations were mainly attributed to the increase of low-chlorinated PCDF congeners in gas-phase. By inference, memory effect existing in SCR might be responsible for the increase of PCDD/F levels. PCDD to PCDF ratios in most of the sampling points were >1, suggesting that de novo synthesis is not the dominant formation pathway in the studied incinerator. This study verified that co-incinerating sewage sludge in the MSWI would not elevate the emission levels of PCDD/Fs. If all of the yielded municipal waste is incinerated with adding 5% sewage sludge, more than half of sewage sludge can be disposed safely in Shenzhen.

Influence factors and mass balance of memory effect on PCDD/F emissions from the full-scale municipal solid waste incineration in China

Studies are carried out in two wet scrubbing systems (WSSs) subordinated to two similar full-scale (30 t h−1) municipal solid waste (MSW) incinerators to explore the influence factors and mass balance of memory effect on polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) emissions. The results show that the memory effect on two WSSs notably increases the TEQ concentrations by 13.6 and 3 times, respectively, through increase in the total mass concentration and the proportions of low-chlorinated PCDD/Fs, directly resulting in the PCDD/F emissions of 1# MSW incinerator over the national standard. PCDD/F adsorption/desorption in WSSs is the reasonable acting mechanisms of memory effect. In addition, memory effect mainly influences gaseous PCDD/F emissions by elevating the percentage of PCDFs, while slightly affects PCDD/Fs in residuals. A mass balance of PCDD/Fs is established to further analyze the influence factors of memory effect on WSSs, indicating filling as the largest potential source discharging PCDD/Fs into outlet flue gas. The results pave the way for further industrial optimization of WSSs design, such as the filling materials with less adsorption capacity on PCDD/Fs and more reasonable operation.

Influences of P-N-containing inhibitor and memory effect on PCDD/F emissions during the full-scale municipal solid waste incineration

Influence of inhibition and memory effect on PCDD/Fs are carried out in a full-scale (23 t h−1) municipal solid waste (MSW) incinerator under three conditions. Ammonium dihydrogen phosphate (ADP) is injected into the post combustion zone of incinerator. The results show that the inhibition efficiency of PCDD/Fs in flue gas was 53.34% (71% for TEQ), and ADP possibly also didn't have effect on the chlorination reaction of PCDD/F formation. The memory effect phenomenon, PCDD/F adsorption/desorption, is clearly discovered in the wet scrubber system (WSS), resulting in PCDD/F concentration increased by 6.2–19.9 times. Memory effect also changes the distribution of PCDD/Fs by increasing the proportions of low-chlorinated PCDD/Fs, which is easily to be desorbed because of their higher vapor pressure comparing with the high-chlorinated PCDD/Fs. After renewing the scrubbing solution and cleaning the bottom sludge in WSS, the PCDD/F TEQ concentrations decreases from 0.51 to 0.24 ng I-TEQ Nm−3, further mitigating but still not enough to eliminate the memory effect because the PCDD/F desorption of wall and scrubber fillings in the WSS. The results are paving the way for further industrial optimized design of WSS and assist in controlling the PCDD/F emissions from MSWI.

Suppressing formation pathway of PCDD/Fs by S-N-containing compound in full-scale municipal solid waste incinerators

The emission of polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) is a serious concern from municipal solid waste incineration (MSWI). The utilization of inhibitor is an effective method to inhibit the formation of PCDD/Fs. In the present study, the thiourea is used as an effective inhibitor in two full-scale MSW incinerators, and the suppression mechanisms are investigated in detail. After the injection of thiourea, the total PCDD/Fs emission factor decreases from 6.19 and 7.89 mg/t MSW (0.13 and 0.18 mg I-TEQ/t MSW) to 1.35 and 1.34 mg/t MSW (0.029 and 0.026 mg I-TEQ/t MSW), respectively for incinerator A and B. In the post-combustion zone, the contribution of three pathways on PCDD/Fs formation is found to be in the order of de novo synthesis > chlorophenol (CP) route formation > chlorination of dibenzofuran (DF) and dibenzodioxin (DD). The S and N in thiourea poison the catalytic metals, thus significantly hindering the de novo synthesis of PCDD/Fs. Since metal catalysts for precursor-formation are not as crucial as for de novo synthesis, the thiourea has less suppression effect on CP-route synthesis, which is identified from the reduction of signal intensity of CP-route congeners. In addition, the chlorination of DF/DD is also observed to be suppressed, indicating the transformation of Cl2 to less activate HCl caused by thiourea. This study provides a robust basis to promote the industrial application of inhibitor to control the emissions of PCDD/Fs from MSW incinerator.

Estimating source strengths of HCl and SO2 emissions in the flue gas from waste incineration

HCl and SO2 emission is one of the major concerns related to municipal solid waste incinerator (MSWI). In this study, a material flow analysis model was developed to estimate the HCl and SO2 concentrations in the MSWI flue gases (FGs), and their concentrations in the full-scale MSWI were monitored. The calculated concentrations of HCl and SO2 in the FG were 770–1300 mg/Nm3 and 150–640 mg/Nm3, respectively, in close agreement with the monitored values. More than 99% of Cl and 92% of S from the FG were captured into solid residues by the air pollution control (APC) systems. Moreover, since only 48.4%–67.5% of Cl and 21.3%–53.4% of S were transferred to the FG from the municipal solid waste (MSW), it was more reliable to estimate the source strengths and release amounts of HCl and SO2 in the FG based on the amounts of Cl and S in the APC residues (AR) and exhaust gas rather than in the MSW. This simple method is easily applicable and the estimated results could provide scientific basis for the appropriate design and operation of the APC systems as well as corrosion control of heat recovery systems.

Suppression of dioxins after the post-combustion zone of MSWIs

Thiourea was selected as representative of combined S- and N-inhibitors and injected after the post-combustion zone of two full-scale municipal solid waste incinerators (MSWIs) using a dedicated feeder. Firstly, the operating conditions were scrutinised by monitoring the concentrations of SO2, NH3 and HCl in the clean flue gas. The suppression experiment showed that in MSWI A thiourea could reduce the total I-TEQ value in flue gas by 73.4% from 1.41ng I-TEQ/Nm3 to 0.37I-TEQ/Nm3, those in fly ash by 87.1% from 14.3ng I-TEQ/g to 1.84I-TEQ/g and the total dioxins emission factor by 87.0wt.%, with a (S+N)/Cl molar ratio of 9.4. The suppression efficiencies of PCDD/Fs in flue gas and fly ash in MSWI B could be up to 69.2% and 83.0% when the (S+N)/Cl molar ratio attained 7.51. Furthermore, the congener distributions of dioxins were also analysed in the flue gas and fly ash, before and after addition of thiourea, to find cues to some suppression mechanism. In addition, the filtered fly ash was explored by the Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analysis of fly ash. These results suggest that poisoning the metal catalyst and blocking the chlorination are most probably responsible for suppression.

Simultaneous suppression of PCDD/F and NOx during municipal solid waste incineration

Thiourea was tested as a dioxins inhibitor in a full-scale municipal solid waste incinerator with high capacity (34th−1). The suppressant, featuring a high S- and N-content, was converted into liquor and then injected (35kgh−1) into the furnace (850°C) through the inlets already used for Selective Non-Catalytic Reduction (SNCR) of flue gas NOx. The first results show that thiourea reduces the dioxins in flue gas by 55.8wt.%, those in fly ash by 90.3wt.% and the total dioxins emission factor by 91.0wt.%. The concentration of PCDD/Fs was 0.08ngTEQNm−3, below the national standard of 0.1ngTEQNm−3. The weight average chlorination degree of dioxins decreases slightly after adding the inhibitor, indicating that it suppresses both the formation and the chlorination of dioxins. Analysis of fly ash by scanning electron microscope (SEM) suggests that the particle size becomes larger after adding the inhibitor. Further analysis using an energy dispersive spectrometer (EDS) reveals that the sulphur content in fly ash rises, but the chlorine content declines when adding thiourea. These results suggest that poisoning the metal catalyst and blocking the chlorination are probably responsible for suppression. NOx reduction attains 42.6wt.%. These tests are paving the way for further industrial application and assist in controlling the future emissions of dioxins and NOx from MSWI.

Pilot Tests on the Catalytic Filtration of Dioxins

Tests were conducted to study the removal efficiencies (REs) of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from flue gas during a test program involving a pilot-scale catalytic filter (CF) module and a full-scale municipal solid waste incinerator (MSWI). The REs attained with the CF on a side stream and a conventional activated carbon (AC) injection and baghouse filtration system in the full-scale MSWI are evaluated via simultaneous sampling and analysis of both gas- and particle-phase PCDD/Fs. Flue gas without AC is supplied to the pilot-scale CF module for evaluating its RE capabilities. The REs achieved with the CF at 180 °C are 96.80 and 99.50%, respectively, for the gas phase and the particulate contained. The gas-phase PCDD/F RE rises significantly at 200 and 220 °C. The air/cloth (A/C) ratio defined as is the gas flow rate (m(3)/min) divided by the filtration area (m(2)) also affects the PCDD/F RE, especially in the gas phase. At 180 °C, a RE of gas-phase PCDD/Fs of 95.94% is attained with the CF at 0.8 m/min, yet it decreases at higher A/C ratios (1 and 1.2 m/min). A significantly lower toxic equivalency (TEQ) concentration (0.71 ng I-TEQ/g) was measured in the filter dust of the CF module compared to that collected by the AC adsorption system (4.18 ng I-TEQ/g), apparently because of the destruction of gas-phase PCDD/Fs by the catalyst.

Indication of PCDD/F formation through precursor condensation in a full-scale hazardous waste incinerator

This paper gives the PCDD/F fingerprint of boiler and fly ash of a full scale hazardous waste incinerator and demonstrates that, when the waste to be incinerated contains high concentrations of PCBs and chlorinated pesticides, heterogeneous precursor condensation is the dominant PCDD/F formation mechanism rather than de novo synthesis. This is in contrast to full-scale municipal solid waste incinerators, where de novo synthesis has been shown to be the dominant PCDD/F formation mechanism. This paper agrees with earlier predictions based on numerous lab scale experiments.